Apparatus and method for optical raster-scanning in a micromechanical system

Abstract

A method of operating a micromechanical scanning apparatus includes the steps of identifying a radius of curvature value for a micromechanical mirror and modifying a laser beam to compensate for the radius of curvature value. The identifying step includes the steps of measuring the far-field optical beam radius of a laser beam reflected from the micromechanical mirror. The measured far-field optical beam radius is then divided by a theoretical far-field optical beam radius reflected from an ideal mirror to yield a ratio value M. An analytical expression for M is curve-fitted to experimental data for M with the focal-length as a fitting parameter. The focal-length value determined by this procedure, resulting in a good fit between the analytical curve and the experimental data, is equal to half the radius of curvature of the micromechanical mirror. The micromechanical scanning apparatus is operated by controlling the oscillatory motion of a first micromechanical mirror with a first micromechanical spring and regulating the oscillatory motion of a second micromechanical mirror with a second micromechanical spring.

What is claimed is:  
     
       1. A method of operating a micromechanical scanning apparatus, said method comprising the steps of: 
       identifying a radius of curvature value for a micromechanical mirror; and  
       modifying a laser beam that impinges upon said micromechanical mirror so as to compensate for said radius of curvature value so as to improve the optical resolution of said micromechanical scanning apparatus.  
     
     
       2. The method of claim  1  wherein said identifying step includes the steps of: 
       acquiring a measured far-field optical beam radius for a laser beam reflected from said micromechanical mirror;  
       dividing said measured far-field optical beam radius by a theoretical far-field optical beam radius reflected from an ideal mirror to yield a ratio value M;  
       curve fitting an analytical expression for M to experimental data for M with focal-length as a fitting parameter; and  
       multiplying said focal-length of said curve fitting step by two to establish said radius of curvature.  
     
     
       3. The method of claim  2  wherein said dividing step includes the step of dividing said measured far-field optical beam radius by a theoretical far-field optical beam radius from a perfectly flat, infinitely large theoretical mirror to yield said ratio value M. 
     
     
       4. The method of claim  1  wherein said modifying step includes the step of optically modifying said laser beam to compensate for said radius of curvature. 
     
     
       5. The method of claim  4  wherein said modifying step includes the step of re-shaping the phase front of said laser beam to compensate for said radius of curvature. 
     
     
       6. The method of claim  1  wherein said modifying step includes the step of optically modifying said laser beam within said micromechanical scanning apparatus. 
     
     
       7. The method of claim  1  wherein said modifying step includes the step of optically modifying said laser beam outside of said micromechanical scanning apparatus. 
     
     
       8. The method of claim  7  wherein said modifying step includes the step of optically modifying said laser beam with macroscopic lenses. 
     
     
       9. The method of claim  7  wherein said modifying step includes the step of optically modifying said laser beam through positioning of a display screen. 
     
     
       10. The method of claim  7  wherein said modifying step includes the step of modifying said laser beam with a second micromechanical mirror with a radius of curvature value that is opposite said radius of curvature value for said micromechanical mirror. 
     
     
       11. The method of claim  1  further comprising the step of synchronizing a first micromechanical mirror with a second micromechanical mirror with a modulated light source to produce a displayed image. 
     
     
       12. The method of claim  11  further comprising the step of operating said modulated light source to produce grey-scale images within said displayed image. 
     
     
       13. The method of claim  11  further comprising the step of projecting said displayed image onto the retina of an eye. 
     
     
       14. The method of claim  11  wherein said second micromechanical mirror moves at a sub-harmonic frequency of said first micromechanical mirror.